Why sewage counts as Category 3 water, who to call in Minneapolis, Portland and Austin, how to clean up safely, and why most policies need a backup add-on.
By the WaterDamageRated team · Facts checked against the sources listed below on November 1, 2026. General information, not professional advice.
With a clean-water leak, the job is mostly drying. A sewage backup has to be treated as a health hazard first. The IICRC, the body behind the ANSI/IICRC S500 water damage standard, says in a 2026 position statement that Category 3 water is grossly contaminated and can contain pathogenic, toxigenic or other harmful agents. Its examples include sewage, and wasteline backflows that originate from beyond any trap, regardless of what the water looks like. Northern Arizona University's water damage guideline, which uses the same categories, adds that Category 2 water that is not removed promptly may be reclassified as Category 3, so a slow cleanup can make a smaller problem worse.
That changes the order of work. The statement quotes the S500 standard as saying that for Category 2 or 3 water, remediation should happen before restorative drying, and that where necessary an indoor environmental professional should be used to assess contamination. EPA's water damage cleanup table covers clean water only. For water contaminated with sewage or chemical or biological pollutants, EPA says OSHA requires protective equipment and containment, that an experienced professional should be consulted if you don't have expertise in contaminated-water cleanup, and that fans should not be used until the water is known to be clean or sanitary.
Austin Water's advice for a backup is to stop using any water and call its dispatch office at 512-972-1000, then remove the cleanout cap to reduce the pressure and limit sewage backing up into the house. It says the cleanout cover is typically 4 inches in diameter and that it is important to know where yours is.
Then find out where the blockage is. The city sewer and your own service line are handled differently:
Each city has its own claims route. Minneapolis says property owners can submit a claim for damages and other costs related to a backup, that sewer crews carry claimant packets, and that fault is generally worked out between insurance companies. Portland directs damage claims related to a backup of the city's sewer system to its Risk Management group, at 503-823-5101. Either way, photographs and receipts will matter.
Portland's Bureau of Environmental Services gives these precautions for anyone cleaning up after a backup:
EPA's flood cleanup fact sheet adds that cleaning products should never be mixed and that you should wear at least an N-95 respirator, goggles and protective gloves. Porous materials are the hard part. EPA says materials that soak up a lot of water, such as drywall, carpets and ceiling tiles, should be thrown away after flooding, and Northern Arizona University's water damage guideline, which uses the IICRC categories, only allows carpet to be kept if it has not been wet with Category 3 water at all.
Portland also suggests hiring a cleanup professional as an option, and Minneapolis suggests considering a professional cleaning company to confirm there are no health hazards left in the basement.
Don't assume your homeowner's policy will pay. The Minnesota Department of Commerce says neither flood insurance nor a typical homeowner's policy covers damage caused by sewer backups, and that owners must buy a separate product or endorsement. Some companies exclude sewer backup that happens at the same time as a flood. After a backup, Minnesota's regulator suggests calling your insurer as soon as you can, preventing further damage if it's safe, photographing the damage, providing a home inventory, checking for loss-of-use coverage if you need to stay elsewhere, and getting written estimates.
When you shop for a policy, the Texas Department of Insurance's comparison worksheet lists backup of sewers and drains as its own coverage item to ask about. More on what standard policies cover is in our insurance guide.
Portland's sewer utility describes a sewer backflow prevention device as a one-way valve installed in the home's drain line, and runs a program that helps pay for installing one for residents of combined sewer areas subject to basement flooding. Under that program the resident owns the device and handles its maintenance and repair, and the property owner is responsible for any future sewer backups at the address after taking part. Austin Water says it is important to know where your property's cleanout is, since removing its cap is how it tells residents to relieve the pressure during a backup. Ask a licensed plumber whether a backflow valve suits your house.
Portland's sewer utility gives cleanup steps for residents, including protective clothing and a bleach solution, or suggests hiring a cleanup professional. For contaminated water, EPA says an experienced professional should be consulted if you don't have expertise in that kind of cleanup.
It depends where the blockage is. Austin, for example, says overflows from defects in the private line are the owner's responsibility, while those from city-owned pipes or severe weather are the city's. Minneapolis and Portland both have claims processes for backups caused by the city sewer.
Usually not on its own. The Minnesota Department of Commerce says a typical homeowner's policy doesn't cover sewer backups and that you need a separate endorsement.
38 companies in 5 areas, scored by the same published criteria.